The present invention relates to methods and apparatus for stabilizing the idle speed of spark ignited internal combustion engine.
Prior U.S. Pat. application Ser. No. 044,328 filed May 31, 1979 discloses a method and apparatus for regulating idle speed of a spark ignited internal combustion engine by control of the ignition timing. In particular, the engine therein described is provided with a lean fuel-air mixture, to favorably influence the engine exhaust emission. The loss in the engine torque attributable to the lean mixture is recovered by providing a relatively high air throughout volume. The nominal ignition timing is relatively retarded, and the timing is advanced by a control circuit to stabillize the engine idling speed at a speed which approximates a desired value.
In German patent disclosure No. 2,221,354 there is described another method for stabilizing idle speed upon the occurrence of changes in engine load. In accordance with the disclosure, the ignition timing is advanced to compensate for increased engine load. Also, in order to compensate for the loss in output which results from a nominal retarded ignition timing, the volume of the mixture charge is increased.
German disclosure No. 2,725,460 discloses a governor wherein the volume of mixture provided to the engine is controlled in order to compensate for changes in engine load. A similar control is described in German disclosure No. 2,756,704. That document describes a system for control of air supply as a function of intake vacuum. Idling speed is increased during starting and warmup by an electrically generated control signal.
German disclosure No. 2,715,408 describes an idling speed governor wherein changes in load are compensated by changes in the volume of fuel supplied to the engine.
A characteristic of all of these prior art systems is that speed stabilization is obtained through variation of only a single engine control parameter. Consequently, the parameter must be varied over a range which is large enough to result in poor engine operation for some engine load conditions, or alternatively, full engine speed stabilization cannot be achieved. It is, therefore, an object of the present invention to provide a new and improved method and apparatus for controlling the idle speed of an internal combustion engine.
It is a further object of the invention to provide such an apparatus wherein such control parameter is varied over a predetermined selected range of values to ensure efficient and pollution free operation of the engine.